Composition of an epoxy resin and 2,2-alkylene bis-2-oxazoline as curing agent

ABSTRACT

M 2 OR 3 N 1 - 3 R H or alkyl C1-4 useful as latent curing agents in polyepoxides to produce epoxy resins; to homopolymerize, or to copolymerize with dithiols; to homopolymerize or copolymerize ethylenically, or any combination of these:

United States Patent 1 Tomalia COMPOSITION OF AN EPOXY RESIN AND2,2-ALKYLENE BIS-2- OXAZOLINE AS CURING AGENT Donald A. Tomalia,Midland, Mich.

The Dow Chemical Company, Midland, Mich.

Filed: Jan. 28, 1971 Appl. No.: 110,752

Inventor:

Assignee:

Related U.S. Application Data Division of Ser. No. 833,765, June 16,1969.

U.S.Cl. ..260/47 EN, 260/307 C Int. Cl. ..C08g 30/14 Field ofSearch...-. 260/47 EN, 2 EN, 18 l IP,83Q TW, 260/307, 59

References Cited UNITED STATES PATENTS 4/ i970 Ranck et al. 260/837Assistant ExaminerT. Pertilla Attorney-Thomas J. Page et al.

R=Hor alkylC useful as latent curing agents in polyepoxides to produceepoxy resins; to homopolymerize, or to copolymerize with dithiols; tohomopolymerize or copolymerize ethylenically, or any combination ofthese:

1 Claim, No Drawings pending application Ser. No. 833,765, filed June16,

BACKGROUND OF THE INVENTION 1. Field of the Invention The polyepoxidesthat can be cured to obtain epoxy resins are well known as are manycuring agents, some of them latent, in the sense that they initiate acure so slowly as to be negligible or nearly so, until the curablemixture is heated. The diheterocyclic compounds of this invention arecuring agents of unusual latency, for polyepoxides. They alsoparticipate readily in a wide range of other reactions that lead topolymeric resins.

2. The Prior Art Feinauer et al., 698 Annalen 174 (1966) have shown thereaction between certain monooxazolines and monoepoxides to producevarious l-aza-4,6-dioxabicyclo-[3.3O octane compounds.

Numerous systems for the curing of polyepoxides are known in the art; byreference, there are incorporated here chapters 5 through 13 of Handbookof Epoxy Resins" (McGraw Hill, New York, 1967) by Lee and Neville,wherein general and particular discussion of the curing of epoxy resinsis presented. U.S. Pat. No. 2,924,571 purports to show the preparationof various 2,2'-alkylene bis 2-oxazolines by the benzene azeotroping ofwater from a mixture of dicarboxylic acid and amino ethanol. The presentinventors have reinvestigated the work set forth inthe said patent andhave found that while the processes there set forth, employing thestated starting materials, lead to products having (so far as thepresent inventors know), at leastsome and perhaps all of the usefulproperties imputed to them, nevertheless, the structures and namesassigned to the supposed products of the patentare consistentlyerroneous. One reading the patent would believe himself led to thepreparation of an alkylene bisoxazoline compound, whereas, in fact,following the. procedures of the patent one obtains, at best, a mixtureof 2- hydroxyethyl amide and certain polyesteramide substances. Thepatent does not enable the preparation of any oxazoline. Recognizingthesignificance of their imputation of error, the present applicantshave scrupulously verified, and have proved, the errorin the prior artpatent.

Kagiya and co-workers (4 Polymer Letters 257) (1966) have reported thepreparation of 2,2'-alkylene or p-arylene bis-2-oxazolines by thereaction of .l ,1 '-alkylene or arylene-dicarbonyl bisdiaziridines withacetonitrile in the presence of sodium iodide.

Various monooxazoline compounds have been shown to be capable ofhomopolymerization under such influence as catalytic boron trifluoride:see Tomalia vet al.,4 Journal of Polymer Science, 2253 (1966). W.Seeliger et al, Edit. 5 Angew. Chem. internat., 875 (1966). Syntheticroutes have been summarized by Wiley et al, 44 Chem. Revs., 447-475.Other recent synthetic developments as well as various polymerizationsare reported by Seeliger et al Edit. 5 Angew. Chem.internat. 875 (1966).

DESCRIPTION OF TH E PRESENT INVENTION The present invention providesbiheterocyclic compounds in which the heterocyclic rings are of five orsix ring atoms and are represented, generically, by the formula in whichRrepresents hydrogen or alkyl of from one to four, .both inclusive,carbonatoms, m, represents an integer, two or three, and n represents aninteger from one tothree, both inclusive.

The compounds homopolymerize under cationic catalytic influence to yieldhighly cross-linked homopolymers that result from opening of theheterocyclic rings. Such polymer-is of thegeneral unit structureAlternatively, or in addition, the present compounds can be causedtopolymerize ethylenically at the site of the ethylenic linkage.

Further, by the activity of the oxazoline or oxazine ring, the instantcompounds react with and bring about cure of a curable polyepoxide toobtain an epoxy resin. As polymers of the instant compounds are, ingeneral, terminated with a .heterocycle of the instant compounds,-suchpolymers arealsocuring agents for epoxy resins.

Thecure of a polyepoxide takeseither orboth of two forms; bybreaking ofthe carbon-nitrogen double bond without ring opening,.,the'heterocyclesof this invention fuse with-at least some-of the oxirane rings of acurable polyepoxide to yield aproduct of the structure in some way actscatalyticallytoinduce thecure of a polyepoxide by opening of the oxirane ring and the setting up of cross-linking etherification', in themanner customary of such polyepoxideinbecomin'g a cured epoxy resin. a

Moreover, the oxazine or oxazoline ring is capable of reaction with amercapto group to give rise to a structure of the polyamide typegenerally represented by the formula in which the broken line representsthe nuclear structure of a dithiol starting material.

Instead of 'a dithiol, hydrogen sulfide or a polythiol can be used. Withhydrogen sulfide, the polyamide is of the general formula 0, I z aorhort ii-Nu onm 5 0?. 1..

whereas with a polythiol above a dithiol there takes place thecross-linking of amide structures with multiple branching from thepolythiol nucleus.

PREPARATION OF THE PRESENT COMPOUNDS The bisalkenyl oxazoline andoxazine compounds of this invention are all easily produced by any of agroup of synthetic routes all of which pass, advantageously, through acyano group; in the sense that, at each molecular site where an oxazineor oxazoline heterocycle is desired, there is provided, as a precursorsite, a cyano. From such site it is, in general, convenient and easy togo onto the desired heterocycle. The only condition believed to belimiting at this juncture is that, with respect to the reactions that goon from the-cyano to the heterocycle, preferably the cyano be the mostreactive or only significantly reactive site: or, if any other site onthe starting cyano compound be more reactive than cyano, then knownalternative procedures must be considered.

It is not difficult, and in the laboratory work carried out in thecompletion of the instant invention, it has become routine, to preparethe instant compounds with elegance and high purity. However, it ispointed out that for at least their reactivity as monomers andcomonomers and curing agents, such elegance is not required. Mixedstarting materials can be used to give mixed products all within thesingle class, or genus, of such compounds as hereinbefore set forth, allwill function as indicated. Stoichiometry of starting materials can bepermitted to vary in such fashion that substantially more, or somewhatfewer, average, oxazine or oxazoline heterocycles. appear, per molecule,than precisely two as above indicated; and for. at least theirreactivity as monomers and comonomers and curing agents, all willfunction as indicated. Sirnilarly, the position isomery of substituents(butnot within the nuclear structure of the oxazine or oxazolinemoieties) may vary widely without impairing the products of thisinvention.

Many synthetic routes are known by which to provide reactive cyano sitesas desired. Reference is here compound made, to incorporate the Mowryreview in 42 Chemical Reviews 189-283. Methods'there'set forth in detailsuf- .oxazine (6-membered) ring will be determined by the chain lengthand structure of the acyclic substituent and is in each case entirelyoptional with the synthesis chemist. ln many applications where the solecriterion to be met is that according to this invention there be.provided a superior curing agent for an epoxy resin or a superiorcomonomer, mixtures of oxazolines and oxazines will be as satisfactoryas, or in some applications, more satisfactory than, compounds of highindividual purity.

The most forthright route, procedurally, involves reactions of amechanism which, when set out in detail, appears complicated; butprocedures remain simple. This route involves causing a reaction of thecyano precursor with a loweralkylene chlorohydrin in the presence ofhydrogen chloride, and upon the completion of that reaction, cyclizingthe resulting intermediate with a substance, usually a base, which is anacceptor for the elements of hydrogen halide, such as triethylamine,trimethylamine, or an alkali metal hydroxide. With ethylene chlorohydrin(2- chloroethanol) this procedure leads to the oxazolines whilst withtrimethylene chlorohydrin, (3-chloro-lpropariol) itleads to theoxazines: and with a mixture of chlorohydrins, a mixture ofheterocycles.

Alternative to the foregoing, yet starting from the cyano structure, agroup of related synthetic routes proceeds by a first oxidation of thecyano to the carboxyl, as in the presence of sulfuric acid and underprotonating conditions. Upon completion of the conversion to thecarboxyl form, the resulting intermediate is 'then converted to the acylhalide, such as the chloride; in one convenient method this conversionis brought about by reaction of the carboxyl compound with thionylchloride. Acyl halides other than the chloride are available; and can beused.

From the acyl halide form, various optional routes proceed. The acylchloride reacts readily with aziridine (ethyleneim ine) to obtain anintermediate which, in turn, in the presence of basic hydrogen chlorideacceptor, cyclizes to the desired oxazoline structure.

Similarly, azetidines are used. The unsubstituted material is not wellknown to the present inventors, but numerous azetidines in which theheterocyclic ring has been stabilized by substituents give good results.In general, substituents on the carbon atom of azetidines appear in thefinal oxazine products as substituents upon the corresponding carbonatoms.

From the acyl halide, another synthetic route requires reaction of theacyl halide with an amino alcohol, to produce an acyclic intermediatewhich, from the amino alcohol, is hydroxyl terminated and which,

under moderate conditions of dehydration, gives the desired cycliccompound. The identity of the cyclic compound is determined by thenumber of linear carbon atoms between the hydroxyl and the amino groups.if two, the product is an oxazoline. If three, the product is anoxazine: if a mixture, a mixed product results. In another method adiacyl chloride of an unsaturated dicarboxylic acid is reacted, at near0 C and absent water, with aziridine under conditions for the acceptanceof the elements of hydrogen chloride, to produce the corresponding bisacylaziridine. Excess exotherm is to be avoided.

The bisacylaziridine is then taken up in dry acetone, together withsodium iodide catalyst, and is refluxed over several hours to rearrangethe acylaziridine to obtain the bisoxazoline.

The cyclizing reactions in which precursor substances are converted intothe oxazoline compounds of the present invention are, in generalexothermic and, in general, they do not require extreme conditions to beinitiated. As such cyclizing reactions go forward, there is at leastsome tendency for competing reactions to take place in which, in amanner that has not been fully studied, polymeric substances appear tobe formed. Such polymeric substances tend to be gummy or weakly resinoussubstances and of no presently recognized value, and are not desired.Higher temperatures favor the production of such polymeric substances,and, accordingly, it will oftentimes be desired to maintain reactiontemperatures as low as is convenient. Accordingly, the addition ofcyclizing agent will oftentimes be carried out slowly, portionwise, andwith the resulting reaction mixture cooled or chilled.

Good results are usually obtained when the cyclizing reaction accordingto the present invention is carried out at a temperature between 30 Cand +40 C. Within this range, at or beyond the lower limit the cyclizingreaction goes forward very slowly; above the upper limit competing andprobably polymerizing reactions go forward at such rate as to bewasteful. A preferred temperature range will vary somewhat according tothe precise identity of the precursor substance to be cyclized and alsoaccording to the. identity of the cyclizing agent; but, in general, acyclizing reaction temperature of 0 to C will be preferred. When suchtemperatures are employed, however, it may at times be advantageous todrive the last aspects of the reaction to completion by the applicationof moderate heat or at least the removal of cooling for a terminalinterval of reaction time.

The reaction can be carried out in the absence of liquid reactionmedium. However, there is considerable tendency for employed materials,especially very pure materials, to crystallize; in this condition,-theorderly procedure of the cyclizing reaction may be inhibited, and itwill usually be desired to prevent or diminish crystallization by theaddition of some liquid solvent that is inert to the reaction that istaking place, whereby to maintain an entire reaction mixture in theliquid phase until reactions are substantially complete. Solvent can bechosen for such volatility that it is thereafter readily stripped away.

The precise relationship between the amount of reactant to be cyclizedand the capacity of the'vessel in which cyclization is carried out isnot critical. In general, the inventory of starting material and thecapacity of the vessel in which cyclization is to be carried out shouldbe such that good, thorough, prompt, and complete agitation, such asstirring is convenient.

In general, the atmosphere within the vessel in which cyclization takesplace is not critical and may be air. It may also be air saturated withvapors of a volatile solvent. When cyclodehydrohalogenating, as in theinstance of a chloroalkylamide or chloroalkylamidate, skilled chemistswill at once recognize that the ambient atmosphere must not be richlysupplied with hydrogen halide from outside source, since it wouldcompete in the cyclizing reaction.

The starting amide or amidate compound to be cyclized can be obtained asan article of commerce and supplied as an existing entity to thereaction vessel. Alternatively, and conveniently, when desired, thestarting material that is to be cyclized can be prepared in the samevessel in which it is subsequently cyclized, such preparation takingplace immediately or shortly prior to the cyclization reaction ifdesired. The reaction conditions necessary to prepare thechloroalkylamide or amidate or the hydroxyalkylamide are closely similarto those employed in the cyclization, and such in situ preparation maybe preferred.

Upon the completion of the synthesis of compounds according to thisinvention, work-up, that is to say, the separationand sufficientpurification of the resulting products is not difficult. Mostadvantageous procedures will be determined upon the basis of the exactpreparatory procedures observed. Thus, when hydrogen halide acceptorreacting with the elements of hydrogen halide obtains a water-solubleproduct, the entire reaction vessel contents can be, if desired, mixedwith water and thoroughly stirred to wash the reaction vesselv contents;typically, the resulting mixture separates promptly into an aqueous andan organic layer, product being predominantly in the organic layer.

Distillation can be employed to separate and purify product according tothis invention, and the bulk of material necessary to be distilled cansometimes be reduced by such prior water washing.

Crude or partially purified product sometimes gives evidence that thedesired product of the invention is a solid. In such instance, vacuumdistillation is often of use in purification of product; but also, it isat times useful to take crude product up in and recrystallize it fromsolvent. At least in laboratory quantities, ordinary solvents give goodresults, such as a mixture of four parts diethyl ether and one partacetone by volume. lsopropanol is also at times used with good resultsto obtain a recrystallized solid product.

THE USES OF THE PRESENT INVENTION The bioxazoline or bioxazine compoundsof this invention homopolymerize under protonic catalyticinfluence togive self polymers that are useful as plastics. Any of various catalystscan be used. One convenient and very effective catalyst is the borontrifluoride adduct of the monomer. A monomer of this inventionusually'takes up boron trifluoride in quantity sufficient that it can beused in very dilute form with unmodified monomer to catalyze thepolymerization. When a 1:1 molar BF -monomer adduct is formed, as isoften the case, one mole percent of it in a mixture to be polymerized isusually sufiicient to catalyze the polymerization. It can, if desired,be prepared in situ by passing gaseous BF, over. the surface of astirred monomer composition. If prepared other than in situ it is to bemaintained dry and out of contact with oxygen.

The catalyzed bioxazoline compound or mixture of such compoundspolymerizes promptly upon being heated. The resulting polymers, absentplasticizing agents, are glassy, hard, and of color represented by thatof the unpolymerized material. They are highly 1 crosslinked andmanifest the thcrmoset and insolubility properties characteristic ofcrosslinked polymers.

' In another embodiment, a mono-oxazoline compound of the prior art (seeTomalia et al., cited above) is mixed in, as comonomer, with a crosslinking proportion of a bioxazoline or bioxazine compound of thisinvention, and the resulting mixture is catalyzed, as above, and heatedto obtain a copolymer of the oxazoline and bioxazoline compounds. Therelative abundance of the two kinds of monomer is adjusted to give aproduct of desired extent of cross linking. Manipulative procedures areas those set forth above for the homopolymers.

Each embodiment of the foregoing described products of the presentinvention is useful as a reactive curing agent to cure a curablepolyepoxide to obtain an epoxy resin. In this use, it is not necessaryto produce the products of this invention with a high degree of purityin such matters as position isomery; or whether highly purified oxazinesor oxazolines. Mixed products of this invention together with modestamounts of naturally occurring side products are of value and in someinstances may be preferred, in the curing of polyepoxides.

For such use, the present diheterocyclic compounds bring theextraordinary advantage that, through highly effective as co-reactivecuring agents, they can be mixed with the curable polyepoxide in advanceand left together with it over prolonged periods of time without cure ofthe epoxy, provided only that the mixture be protected from curingtemperatures, namely, temperatures in excess of about 100 C.

For one embodiment of such application, the amount of oxazine oroxazoline compound to be employed is calculated upon the basis that, inthe curing reaction, one oxazine or oxazoline ring can react with oneoxirane ring, and the reactants are to be supplied in quantities suchthat about this relative proportion of the substances is supplied. Goodresults are obtained when polyepoxide is supplied in an amount in modestexcess of that required for exact stoichiometric cure.

When either or both materials are liquids or are viscous materials ofviscosity low enough to admit, a curable mixture can be prepared bycombining the polyepoxide and the diheterocyclic compound of thisinvention and mixing them intimately together. When viscosities are toogreat, or either or both substances are solids, they can be warmed totemperatures approaching 75 C. or a little higher, without risk ofuntimely cure when the products are combined.

1 ln orderto combine intimately a polyepoxide and a diheterocycliccompoundof this invention when the substances employed are in physicalform that does not readily admit of mixing them, it will usually bepreferred to dissolve one or both first in a volatile solvent, and tocombine the solvent solution with either of the other of the reactantsor with its solvent solution, and, if solvent present is objectionable,subsequently volatilize and remove solvent as by distillation. lnanother procedure, a known reactive viscosity lowering additive such asbutyl glycidyl ether or phenyl glycidyl ether or a liquid monooxazine ormonooxazoline can be added to either or both of the reactants, in anyquantity necessary to reduce viscosity to the point that the dilutedsubstances can be mixed together. In some applications the resins curedfrom precursors containing a reactive diluent are of inferiorproperties. Those skilled in the art will be able to effect thecombining of the reactants according to this invention satisfactorily.

It has been noted hitherto that the difunctional or approximatelydifunctional products of this invention can be self-polymerized orcopolymerized with polyepoxides. It follows, then, that in concentrationratios numericaliy remote from stoichiometric ratios, the mixture of aproduct of this invention with a polyepoxide yields a composition that,under suitable catalytic influence, forms a resin.

The present invention, then, comprehends mixtures of polyepoxide curableto obtain an epoxy resin with heterocyclic compound of this inventionwith the substances present in equivalent weights or with polyepoxide inmodest excess. In such mixtures in which the polyepoxide is moreabundant, the adduct of heterocycle and oxirane hitherto noted as ofcatalytic activity in curing an epoxide performs that function to curethe polyepoxide catalytically, with co-reaction of the instantpolyheterocyclic products whereby they become integral moieties of theresulting polymer.

The instant compounds, while not well adapted to form ethylenichomopolymers, form copolymers with other ethylenic substances of widevariety. Among the comonomers that are well adapted to be used informing ethylenic copolymers of this invention are butadiene,2,3-dimethyl-1,3-butadiene, isoprene, piperylene, 3-furyl-l,3-butadiene,3-methyl-l,3-butadiene, chloro-l,3-butadiene, 2-bromo-l ,3-butadiene,2-chloro-3-methyl-l ,S-butadicne, styrene, pchlorostyrene,p-methoxystyrene, a-methyl-styrene, vinylnaphthalene, acrylic acid,methacrylic acid, methyl acrylate, ethyl acrylate, methyla-chloroacrylate, methyl methacrylate, ethyl methacrylate, butylmethacrylate, methyl ethacryiate, acrylonitrile, methacrylonitrile,methacrylamide, methyl isopropenyl ketone, methyl vinyl ketone, methylvinyl ether, vinylethinyl alkyl carbinols, vinyl acetate, vinylchloride, vinylidene chloride, vinylfurane, vinylcarbazole,N-vinyl3-morpholinone, vinyl formate, maleic acid, itaconic acid,furnaric acid, crotonic acid, allyl alcohol, vinylfluoride,2-chloroallyl alcohol, l-allyloxy-3- chloro-Z-propanol,N-vinylsuccini-mide, N-tertiarybutyl acrylamide, N-tertiaryoctylacryl-amide, 1,2- dicloropropene-Z l ,2-dichloropropeneltrichlorosytrene, tetrachlorostyrene, pentachlorostyrene,o-methylstyrene, m-methylstyrene, pmethyl styrene,p-tertiarybutylstyrene, p-isopropylstyrene, p-phenylstyrene,p-benzoylstyrene, pcyanostyrene, m-nitrostyrene,m-trifluoromethylstyrene, m-fluorostyrene, m-tertiarybutylstyrene,

stearoylstyrene, oleoylstyrene, linoleoylstyrene, avinylnaphthalene,Bvinylnaphthalene, l-(a-naphthyU- propenel 2-( a-naphthyU-propene-l2-(a-naphthyl)- butene-2, 3-(a-naphthyl)-pentene-2, 2-bromo-4-trifluoromethyl-styrene, B-bromo-a,fl-diiodostyrene,B-bromo-p-methyl-styrene, [3-bromo-p-dinitrostyrene,m-secondarybutylstyrene, a,B-dibromostyrene, 3,3- dibromostyrene,a-chloro-2,4,6tri-methylstyrene, a-

chloro-2,3,4,6-tetramethylstyrene, fi-chloro-onitrostyrene,l-chloro-2-(p-tolyl)-l-butene, 4(1- chlorovinyl)-anisole, 2-(l-chlorovinyl)-4-methylanisole, l-chloro-4-vinylnaphthylene,4(l-chlorovinyl)-2-isopropyl-S-methylanisole, 4(2-chlorovinyl-2-isopropyl-S-methylanisole, p-cyclohexyl styrene, 2-ethyl-l-phenyl-l-butene, 3,5-diethyl styrene, 4-fluoro-3-trifluoro-methyl-a-methyl-styrene, a,a-trifluoro-mpropenyltoluene,2-isopropyl-5-methyl-4-vinyl anisole, 2methyl-3-phenyl-2-pentene, methylstyryl ether, N,N- dimethyl-m-vinylaniline, Z-(a-naphthyU-Z-butene, 1,1-diphenyl-ethylene, propenyl benzene, stilbene, lvinylacenaphthene,p-vinylbenzonitrile, p-vinylbiphenyl, 2-vinylfluorene, 6-vinyl-l ,2,3,4-tetrahydronaphthalene, p-vinylphenetole, vinylbutyrate,vinylbenzoate, vinylquinoline, 2-vinyl-pyridine, 2-methyl-5-vinylpyridine, 4-vinylpyridine, N,N-diallyalcrylamide, diallylamine,diallymethacrylamide, 2,5-dimethyl-3,4- dihydroxy-l ,S-hexadiene,2,5-dimethyl-2,4-hexadiene, divinylbenzene, divinyl ester of diethyleneglycol, trivinyl benzene, 2,7-dimethyl-1,7-octadiene, 1,7-octadiene,p-diisopropenylbenzene, 1,3,5-triiso-propenylbenzenep,p'-diisopropenyldiphenyl, i,l,3,3-tetrallyl- 1,3-propanediol,1,1,3,3-tetramethallyl-l,3- propanediol, 4,6-dimethyl-4,6-dihydroxy-l,8- nonadiene, 2,4,6,8-tertramethyl-4,6-dihydrxy-l ,8- nonadiene,nonadiene-l ,8,2,8-dimethylnonadiene-l ,8, acetyl triallyl citrate,ethylene, propylene, and Maleic anhydride.

The polymers are typically of K-values according to Fikentscher of fromabout 2 to about 200.

The preparation of such polymer is relatively routine in the art ofproducing ethylenic polymers; it is favored by such free-radicalcatalysts as 2,2-azobis (Z-methylpropionitrile) (sometimes abbreviatedAIBN) or the organic peroxides. The polymers manifest the propertiescharacteristic of the ethylenic non-polymer precursor compounds in that,after ethylenic copolymerization, they are very active curing agents forpolyepoxide to obtain epoxy resins in the structure of which thecopolymeric backbone becomes a major constituent, the cured resinscharacterized by dense cross linking arising from the polyoxazoline oroxazine structure of the curing agent.

Also, in fashion very similar to that of the nonpolymerizedalkenylbisoxazoline or oxazine structures, via the oxazine or oxazolinemoieties, the instant ethylenic copolymers form interpolymers withhydrogen sulfide or with polythiols.

The preparation of such interpolymer may be carried forward to onlypartial consumption of the oxazine or oxazoline groups, such as a thirdto a half of them, and those remaining are capable yet of curing apolyepoxide to obtain an epoxy resin which, under these circumstancesmay, in the cured form, be regarded as a further interpolymer.

A polythiol to be employed is a compound of the formula wherein R" is ofthe scope of R, as defined above, or can additionally be cycloalkyleneof from 4 to 7, both inclusive, carbon atoms or substitutedcycloalkylene of from 5 to 12, both inclusive, carbon atoms, or phenyl,and k is from lto all available substituent sites on R", and typically2.

Hydrogen sulfide, while not a dithiol, is a compound that presents morethan one hydrogen atom each active and each bound to sulfur; and theseare the characteristics of a compound that will react as comonomer inthis invention. Hydrogen sulfide, therefore, is a comonomer to be usedas are the dithiol compounds.

As noted hereinbefore, when either the thiol or oxazoline comonomer isemployed in excess, the'excess provides chain-terminating mercapto oroxazoline moieties. From the reactivity of such terminal groups, thecopolymers of this invention thus produced can be used to react withl,2-polyloweralkylepoxide compounds that are curable to obtain epoxyresins; and by such expedient there is produced a product of thisinvention that is a copolymer of the dithiol-oxazoline type modified bycontaining also epoxy resin moieties.

The relative amount of thiol compound or bis-oxazoline compound for suchepoxy resin copolymers can be varied from that equimolecular with thedithiol compound to an amount which, with respect to the conventionalpolymer formula, can be expressed as y n when 0 n 2.

As is usually true in the polymer art, the value of y in known only asan average value with a range of deviations; but the exact determinationof these matters is not critical so long as the products of theresulting polymer are satisfactory for their purpose. In general, valuesof y will usually lie in the range of from about 30 to a few thousand,perhaps 4 or 5 thousand, and typically in the range of from about 50 to250. Values in these ranges can be used for guidance in conductingsimple range finding tests to fix a precise value of n to obtain apolymer product of any desired range of properties.

Illustrative of the polythiols to be used in this invention aremethanedithiol; l,l-propanedithiol; 1,1-dimercaptoisooctane;2,2-propanedithiol; 3,3-pentanedithiol; a,a-toluenedithiol;1,2-ethanedithiol; trimethylene-1,3-dithiol; 1,2-propanedithiol; 1,4-tetramethylenedithiol; 2,3-butanedithiol; 1,5-pentamethylenedithiol;2,2-dimethylpropanedithiol-1,3; 1,fi-hexamethylenedithiol;1,2-hexanedithiol; 01,0- decamethylenedithiol;2,6-dimethyloctanedithiol-3,7; 2,6-dimethyloctanedithiol-2,6;pentadecanedithiol-7,8; octadecamethylene anal-dithiol;1,2-cyclohexanedithiol; l,l-bis(mercaptomethyl)cyclohexane; 3,4-thiophenedithiol; propanetrithiol-l,2,3; neopentanetetrathiol;dithiocatechol; dithioresorcinol; dithiohydroquinone;4,5-dimethyldithioresorcinol; 2,4- dimethyldithioresorcinol;4-ethyldithioresorcinol; 2,5- dichlorodithioresorcinol;1,4-naphthalenedithiol; 1,5- naphthalenedithiol; 2,6-naphthalenedithiol;2,7- naphthalenedithiol; 2,2'-dimercaptobiphenyl; and 4,4-dimercaptobiphenyl.

A polyepoxide comonomer to be employed in this invention is a compoundof the general forumla wherein l p and L is a polyepoxide nucleusstructure. Typical such nuclei as of the above formula include(isopropylidenebis(phenyleneoxymethylene)) or its poly-brominatedderivatives, such as the l to 4 brominated derivatives. Alsom-(methylenyloxy)phenyl poly(((methyl-enyloxy)phenylene)methylene) amongother routine and well known structures in the art of polyepoxides thatare curable to obtain epoxy resins. In particular, any curablepoly-l,2-epoxide that is an artior polyoxheated and copolymerized onlypartially, to obtain an intermediate material of average molecularweight severalfold greater than that of the starting materials but yetrelatively reactive with polyepoxides in further polymerizationreactions. This material can be held for useful intervals of time afterpreparation and before use. It can be regarded as a prepolymer."

Such prepolymer can be employed in various ways.

By itself it can be modified as by the addition of fillers, coloringmaterials, opacifying or reflective materials, and the like, and then,by further heating a reaction temperature, fully polymerized withcapture of the additives within the resulting polymeric mass.

In another embodiment, it can be mixed and blended with a polyepoxidethat is curable to obtain an epoxy resin, and the resulting mixtureheated to cure to obtain a useful interpolymeric resin of recurringmoieties derived from the indicated starting materials. The exactproperties of the resulting cured resins depend upon the relativeabundance of starting materials, and also upon details of cure cycleobserved.

The starting materials can be employed in any ratio of relativeabundance in such polyoxazoline-polythiolpolyepoxide mixture, providedthat neither polythiol nor polyoxazoline is supplied in amount less thanten percent by equivalent weight of total mixture. Ratio of polyepoxidecan also vary widely provided that not more than 75 percent of totalmixture, by equivalent weight, is such polyepoxide.

In general, such interpolymers of larger polyepoxide content tend to becross-linked and thermosetting, and thus insoluble and infusible; whilethose of very low polyepoxide content or none tend to be fusible and ofat least limited solubility.

in general those in which prepolymerization was limited and theprepolymer units relatively small, other things being equal, tend toyield more highly crosslinked epoxy interpolymers; whilst those in whichprepolymerization was extensive and the polythiolpolyoxazolineprepolymer units relatively large tend to yield less highly crosslinkedepoxy terpolymer products.

By the application of the foregoing aspects of rationale, polymerchemists can greatly reduce any necessary simple range-finding testsrequired to perfect a desired embodiment of this invention.

While all the compounds thus comprehended are comonomers to be usedinthis invention, those of sim pler molecular structure will, ingeneral, be preferred, as being easier and less expensive to produce.

In the choice of monomers with respect to the synthesis of polymer, amixture of substances within the generic statement above but ofdissimilar identities may be chosen, to obtain a product representingproperties representing the polymer derived from such monomer mixture.

In the polymerization of the instant polythiol copolymerizable mixtureof comonomers, the oxazine or oxazoline undergoes ring opening betweenthe oxygen and the carbon atom in position number five,in theoxazolines; that is, the carbon atom adjacent the ring oxygen andseparated by another ring carbon atom from the ring nitrogen. As thenitrogen accepts hydrogen from the copolymerizing mercapto group, theformerly doubled bond between nitrogen and the carbon atom in positionnumber two, that is, the carbon atom between the oxygen and thenitrogen, breaks and remains as a single bond; the available valencesthen being used to bind the hydrogen, mentioned, and to bind the oxygenin a carbonyl group whereby an amide linkage is formed. The sulfur fromwhich mercapto hydrogen has gone to the nitrogen then bonds with thenumber five carbon atom by the valence left upon ring opening.

The chain thus propagating can, if desired, be terminated predominantlywith either oxazoline groups that have not undergone ring-opening, orwith mercapto groups that have not been split, by the simple expedientof supplying either reactant, as desired, in slight excess overequivalent. if the reactants are supplied in exact stoichiometricamount, the chains tend to be terminated by the indicated groups; butwith no quantitative predominance of one over the other.

The polythiol polymers of this invention, then, are represented by thegeneric structure These polymeric products, when in liquid form, areadapted to be used as curing agents to cure polyepoxides to obtain epoxyresins. The mechanism by which such cure of epoxy resins is accomplishedis not known; but a polymer of this invention may be used in admixturewith such polyepoxide in quantities from l0 percent to percent of eithermaterial, by weight of total mixture; and the resulting mixtureundergoes some chemical reactive process that is not completelyunderstood by which the polyepoxide cures; and each of the polyepoxideand the polymer of this invention loses its individual identity in theresulting modified epoxy resin.

The epoxy resins thus cured have the properties of typical cured epoxyresins, including adhesivity, hardness, and mechanical strength; thoseof higher content of the linear poly-secondary amides of this inventiontend to manifest the modification of properties towards those of theunmodified polyamides; those of higher polyepoxide derivative contenttend to manifest modification of properties towards those of theunmodified epoxy resins.

The resulting resins appear to be highly cross-linked and of excellentmechanical, thermal, and electrical properties and of excellentresistance to solvent attack, uitraviolet degradation and corrosion ofmetal substrates.

BEST MODES or N ,N-bis-(Z-chloroethyDfttHiiiiiid, the s ti'ucture ofwhich is confirmed by infrared and nuclear magnetic resonancespect'r'ififi."

Of this fumaramide, 175 grams (0.735 gram mole) is added to and mixedwith a solution of 34.1 grams, 1.68 gram mole, of potassium hydroxide in30 milliliters 95 percent ethanol. The resulting reaction mixture isthen refluxed for hours and filtered hot to remove potassium chloride ofreaction. The resulting filtrate is warmed to vaporize and removeportions of solvent. Thereupon, from remaining portions of solvent awhite, crystalline precipitate settles out of solution. The crystallineprecipitate is separated out with no attempt to scrub for maximum yield.The product proves to be 80 grams of a white, crystalline material, 48percent of theoretical yield. The product 2,2'-(vinylenebis)-2-oxazoline melts at l86l 89C.

EXAMPLE 2 In procedures much like those foregoing but using 2-methylaziridine, a methyloxazoline product is vobtained.

In more detail, a solution of 91.2 grams, 1.6 gram moles, of2-methylaziridine in 100 milliliters dichloromethane is added by drops,with stirring, and with chilling to a temperature not above 25 C., to asolution of 115.3 grams, 0.754 mole, fumaryl chloride in 280 millilitersdichloromethane. The resulting mixture is stirred at room temperaturefor 1.5 hours, during which time a crystalline product is formed in, andsettles out of, the reaction mixture. Product is recovered byfiltration, washed with dichloromethane and dried over a suction funnelfilter. In an attempt to ascertain a melting temperature, thisintermediate substance (N,N'-bis-(2-chloropropyl) fumaramide) decomposesto a red liquid at 215220 C.

Of this intermediate, 200 grams, 0.75 gram moles, is added in oneportion to a solution of 90 grams potassium hydroxide in 300 millilitersof percent ethanol. The resulting reaction mixture is refluxed for twohours and thereafter filtered hot. From the liquid filtrate, part of thesolvent is vaporized and removed to concentrate the filtrate; and fromit, a crude product precipitates. Yield is 94.7 gram, 49 percent byweight of starting materials. Product is taken up in and recrystallizedfrom n-hexane to yield a crystalline product in the form of whiteneedles, melting in the range of 50-64 C. The assigned structure isconfirmed by infrared spectrum and nuclear magnetic resonance spectrum.

EXAMPLE 3 2,2-( l ,3-Butadienylenebis)-2-Oxazoline' This examplerepresents the first of two (which, in turn, are selected from a largernumber of) processes for production of the subject compound. In thismethod, a muconamide is prepared, and cyclized.

Into a 250 milliliter Erlenmeyer flask, with stirring and chilling to atemperature not above 15 C., is placed a solution of 1.40 grams (0.0078gram mole) muconyl chloride dissolved in 15 milliliters chloroform. Tothis, with vigorous stirring, is added a solution of 0.67 grams (0.0156gram mole) aziridine in 30 milliliters chloroform, during a period of 10minutes. fificificompietionbfthidditibfi; flie'resultirigraciion mixtureis allowed to stand, with continued stirring, at room temperature for anhour. In the reaction mixture, an off-white solid forms and settles outas a precipitate. It is separated by filtration and weighed; it is foundto weigh 1.8 grams, 86.7 percent of theory based upon startingmaterials. Its structure is confirmed by infrared spectrum.Recrystallized from ethanol, it produces white crystals melting at218220 C. This is N,N'-bis- (2-chloroethyl)muconamide, an intermediateto the product of this example.

This intermediate (1.32 grams, 0.005 gram mole) is charged into a 250milliliter Erlenmeyer-flash which contains also 30 milliliters of asolution of 0.40 grams (0.010 gram mole) of sodium hydroxide in 95 percent ethanol. The resulting mixture is heated on a steam bath at refluxtemperature for 25 minutes, by which time a layer of crystallinematerial forms and settles to the bottom of the flask. The mixture isfiltered hot, and from the filtrate, well-defined white crystallineplates settle out as the filtrate cools.

The filtrate is allowed to stand in a negative pressure hood toevaporate to dryness. Light yellow plate crystals form in the bottom ofthe vessel. The plates are washed with cold water and allowed to dry,and found to weigh 0.95 grams, 98 per cent of theory.

Not only does the infrared spectrum confirm the structure, but also itproves to be identical with the spectrum of product produced accordingto the next example following.

EXAMPLE 4 In this example, a muconylbisaziridine is formed andisomerized.

Into a 125 milliliter Erlenmeyer flask, with chilling and stirring, arecharged milliliters dry benzene, 2.2 grams (0.2 gram mole)triethylamine, and 0.86 grams aziridine (0.2 gram mole) and, at O5 C.,the resulting mixture is vigorously stirred while 1.8 grams (0.1 grammole) muconyl chloride in 15 milliliters dry benzene are added. Theaddition is made by drops and over a period of 30 minutes: during thistime temperature is held to 8 C. or below. i

In the course of the reaction, triethylamine hydrochloride forms in thereaction mixture and settles out as a precipitate, rendering stirringdifficult. Following the completion of the combining of the reactants,stirring over the ice bath is continued for 2 hours further to carry thereaction to completion.

Thereafter, the mixture is filtered to separate the amine salt. Filtrateis placed in a negative pressure hood and permitted to evaporate todryness in the hood draft; the resulting product proves to be awhite-tan material weighing 2.58 grams, a crude yield of 67 per cent oftheory. The crude product melts at l04-l08 C. it is taken up in, andrecrystallized from isopropanol, and the recrystallized product melts atl l-l 12 C. A published melting temperature for the product is 110 C.

Of this bis-(l,l'-muconyl)-aziridine, 0.2281 grams (0.0013 gram mole) isadded in one portion to a solution of 1.5214 grams reagent grade sodiumiodide in 50 milliliters dry acetone, in a 100 milliliter Florenceflask. The resulting mixture is boiled under reflux for 21.5 hours toisomerize it, and thereafter filtered hot to separate an unidentifieddark, insoluble material. Acetone is allowed to evaporate in draft of anegative pressure hood; and the resulting light yellow plates arethereafter washed with repeated milliliter portions of cold water toobtain 0.1744 grams (76.5 per cent by weight of starting materials) ofbis-2,2'-(l,3-butadienyl-ene)-2-oxazoline product. The product melts at223.226 C. infrared and nuclear magnetic resonance spectra confirm theexpected structure.

EXAMPLE 5 This example illustrates the cure of polyepoxide by theproducts of this invention; the curing is correctly regarded also as acopolymerization.

, Illustrative of the compounds of the instant invention,2,2'-(vinylenebis)-2-oxazoline, product of, Example l, foregoing, ischosen; and the polyepoxide is a widely used commercial product,substantially the diglycidyl ether of bisphenol A.

Of the oxazoline product, 3.52 grams are finely powdered, and the finepowder intimately mixed and stirred into a stoichiometric amount (7.6grams) of the viscous, liquid polyepoxide. The resulting mixture isheated in a a glass vial at C. for an hour and thereafter the vial isbroken away. The resulting copolymeric product is found to be ahomogeneous, tough, hard, strong, amber colored resin, insoluble incommon solvents and believed to be insoluble in all solvents. lt -issingularly resistant to ultraviolet light degradation and exerts unusualprotection from corrosion upon metals coated with it.

lclaim:

1. A latent, heat-curable composition which, when heated at a curingtemperature, reacts to produce a thermosetting, durable resin, whichcomprises essentially a compound of the formula in which R representshydrogen or alkyl of from one to four, both inclusive, carbon atoms andm represents the integer 2, and n represents an integer from one tothree both inclusive in admixture with a phenolic poly-1,2- epoxide thatis curable to obtain an epoxy resin.

